The present invention relates to a tubular body for controlling the flow rate of a fluid such as a fluid transfused into a human body in a measuring system for measuring the blood pressure, for example, a method of such a tubular body, and a flow control device incorporating such a tubular body, and more particularly to a tubular body which can provide a flow passage capable of allowing a fluid to flow at a relatively high rate therethrough in order to fill the fluid in the measuring system before starting to measure the blood pressure, which can provide a flow passage capable of limiting the flow of the fluid to a lower rate for pressure transmission while the blood pressure is being measured, which prevents air from remaining in the flow passage when it is defined to provide a high flow rate, so that it permits the blood pressure to be transmitted accurately, and which is simple in structure, small in size, and can be manufactured at a lower cost, a method of manufacturing such a tubular body, and a flow control device incorporating such a tubular body.
There have recently been developed blood pressure measuring systems for monitoring the blood pressure of patients continuously with time. Such blood pressure measuring systems are widely employed in medical applications.
A blood pressure measuring system generally comprises a fluid bag for supplying the system with a fluid to be transfused such as physiological saline, a catheter to be inserted into the body of a patient where the blood pressure is to be measured, a pressure transducer for detecting the blood pressure through the fluid filled in the system, and a display/recorder for displaying and recording the value of the blood pressure which is produced by the pressure transducer.
To measure the blood pressure of a patient, the catheter is inserted into an artery of the patient, and is then supplied with the fluid such as physiological saline from the fluid back at a very low rate By supplying the fluid to the catheter, the blood is prevented from flowing into the catheter and hence from being solidified. A change in the pressure of the fluid in the catheter is detected by the pressure transducer, and its value is fed to the display/recorder. As a result, the blood pressure condition of the patient can be monitored on a real-time basis.
In order to control the fluid to flow at a desired rate, a flow control device having a flow resistor is disposed in the tube by which the fluid bag and the catheter are interconnected. The fluid is controlled to flow at a low rate by the flow resistor.
To use the catheter on a human body, it must first be flushed with a fluid to be transfused by a process known as priming so that any air remaining in the catheter and the tube connected thereto will completely be removed. Various flow control devices have been proposed which have mechanisms for temporarily increasing the flow rate of a fluid so that the catheter can be primed within a short period of time. See, for example, U.S. Pat. Nos. 4,192,303 and 4,464,179, Japanese Utility Model Publication No. 61(1986)-28624, Japanese Patent Publication No. (1985) 60-57336 Japanese Laid-Open Patent Publications Nos. 56(1981)-8033, and 60(1985)-207638, and U.S. Pat. No. 4,624,662. The disclosed flow control devices are however complex in construction, made up of many components, and expensive to manufacture. They cannot completely be de-aired, and therefore the blood pressure to be measured is prevented from being transmitted accurately because of remaining air in the system. As a result, the measured blood pressure values are subject to errors.
In view of the above drawbacks, the applicant has proposed flow control devices which are simple in structure and have a good de-airing capability, as disclosed in Japanese Laid-Open Patent Publications Nos. 1(1989)-135970 and 1(1989)-160529.
The disclosed flow control devices include a closure member having a first land, and a tubular body having a second land and fitted over the closure member.
For priming these flow control devices, the closure member is manually deformed elastically to space the first and second lands from each other, thus defining a flushing passage therebetween which allows a fluid to flow at a high rate. The fluid can thus be filled into a pressure transmitting system from the flushing passage within a short period of time. For measuring the blood pressure of a patient, the closure member is released of the manual push to close the flushing passage. The fluid is then controlled to flow at a low rate by the resistance produced by an orifice defined through the second land of the tubular body.